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Thread: 5" Flex Hose/Great Customer Service

  1. #1
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    Nov 2016
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    Richmond, VA
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    5" Flex Hose/Great Customer Service

    I have an old Jet 2 hp dust collector that I am converting to two stage. At Oneida's recommendation, I purchased a Super Dust Deputy which has a five inch outlet. I'll be using five inch flex hose. I ordered 25 feet of black flex hose from The Blast Gate Company. The packaged was shipped quickly and arrived in good shape within a few days of the order. But I only received just over 21 feet of hose. I reached out to The Blast Gate Company, and without question or pictures or anything other than an e-mail from me indicating the length of what I received, it agreed to send me five additional feet of hose. This is very good customer service, and I will be loyal to this company. I wanted to pass this on to the forum. By the way, the dust hose is really nice. Very heavy duty.

  2. #2
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    Aug 2017
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    Arlington, TX
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    Glad it worked out for you, and you didn't need 25 feet in one piece.

    -- Andy - Arlington TX

  3. #3
    Join Date
    Nov 2016
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    No, I don't need it in one piece. In fact, I'm going to break it down into component pieces that I will attach with the Magport fittings. When I need a shorter run, I'll use a shorter run. When I need a longer run, I'll add a piece with the magnetic fittings. This is basically an experiment, like almost everything I do in my shop. Hope it works.

  4. #4
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    You'll get better performance from your system by minimizing the length of flex & using smooth wall duct where possible. Flex really kills airflow.

  5. #5
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    SE PA - Central Bucks County
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    Moving the SDD close to the machine being used and using a short hose will maximize your system performance.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  6. #6
    Join Date
    Aug 2017
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    Quote Originally Posted by Frank Pratt View Post
    You'll get better performance from your system by minimizing the length of flex & using smooth wall duct where possible. Flex really kills airflow.
    The difference in pressure drop between 20 feet of 5 inch flex ("wires covered") and equivalent PVC is 0.6" inches of water at 500 cfm for straight duct, no elbows. If you use "wires exposed" flex, the difference in drop from PVC is 1.4".

    The flex I have (from Oneida) has the wires on the outside, and the inside is pretty smooth, so I assume the "wires covered" difference. If you use the kind of flex that collapses to very short lengths (more often in smaller, 4" diameter flex), the latter, greater, "wires exposed" choice is probably more appropriate.

    However, if you use any 90 degree elbows with your PVC duct (R/D=1), those are about 0.25 inches of water in pressure drop each (at 500 CFM & 5" diameter).

    Alternatively, for a pair of 45 degree elbows (R/D=2), the drop is only 0.16 inches per pair (again @ 500 CFM & 5" diameter).

    Calculations are from http://www.freecalc.com/ductloss.htm

    I encourage readers to experiment with the elbow options to see what a difference it makes. Their elbow options appear to be for sheet metal, fabricated elbows, and may not be as accurate for smooth PVC elbows.

    So, for the same length run (rarely true, PVC will often be longer,) by the time you add three 90 degree elbows in the PVC between DC and machine, the "wires covered" flex may actually perform better than equivalent diameter PVC. However, if you use three or less pairs of longer radius 45 degree elbows, the PVC performs better than the flex. Note there did not appear to be a difference between two 45s and one 90 of the same radius).

    This supports at least using flex for the last few feet to the machine (and perhaps between DC and fixed ducting), rather than multiple elbows with PVC, even for "permanent" installations.

    And for those like me that have a portable DC and 10' of flex, you are almost certainly getting better performance than if you put in a fixed duct network. Note: beware of increasing the duct diameter to compensate, which may slow the air velocity below the dust carrying limit, at which point dust starts collecting and solidifying inside the ductwork.

    -- Andy - Arlington TX

  7. #7
    Join Date
    Feb 2013
    Location
    Tippecanoe County, IN
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    Those flex numbers apply only for straight, full stretched condition. Pressure drop goes up as the flex is compressed. When you compress flex the inner diameter is reduced. Pressure drop varies with length and the inverse fifth power of diameter. So even though a compressed hose is shorter the loss in ID dominates.

    You also have to add the dynamic losses for any bends. Any sag gets you tight bends as well as reduced inner diameter.
    Beranek's Law:

    It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person's opinion.
    L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954), p.208.

  8. #8
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    Aug 2017
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    Quote Originally Posted by David L Morse View Post
    Those flex numbers apply only for straight, full stretched condition. Pressure drop goes up as the flex is compressed. When you compress flex the inner diameter is reduced. Pressure drop varies with length and the inverse fifth power of diameter. So even though a compressed hose is shorter the loss in ID dominates.

    You also have to add the dynamic losses for any bends. Any sag gets you tight bends as well as reduced inner diameter.
    David, excellent points.

    But I wonder what "fully extended" really means? Stretched taught? Relaxed?

    The wire helix itself actually reduces diameter as the helix is stretched in length, and conversely increases diameter when the coils are compressed.

    Somewhere in there is a maximum.

    In my mind (and not communicated), I was not considering running flex, draped between supports, across the ceiling to the machine(s). I was thinking of flex on the floor, where the bends are fewer and lazier. I believe a small dust collector is better off rolled around from machine to machine as they are used, and connected with a short (<20 feet, I use 10 feet) flex, than connected to a permanent ductwork hung from the ceiling, with drops to each machine, even if only one machine is used at a time. There is a price for that convenience, and it is in a more powerful dust collector, in addition to the ductwork and blast gates.

    Note that the duct's inside cross section in the bend of a flex becomes non-circular, with both reduced and increased radius sectors of its cross-section, as one side of the duct is compressed, while the other side is stretched in a bend. It's not like the whole duct reduces in diameter in a bend.

    -- Andy - Arlington TX

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